Inventory Buffer Zone Calculator
Size red, yellow and green buffer zones from average daily usage and decoupled lead time. Free, runs in your browser, nothing is uploaded.
Single-item calculator
Your buffer
| Result | Units |
|---|---|
Yellow zone Yellow = 10 × 20 = 200.0 | 200.0 |
Red base Red base = 10 × 20 × 0.5 = 100.0 | 100.0 |
Red safety Red safety = 100.0 × 0.5 = 50.0 | 50.0 |
Red zone Red = 100.0 + 50.0 = 150.0 | 150.0 |
Green zone Green = max(MOQ 0, 10 × 20 × 0.5 = 100.0, 10 × 7 = 70.0) = 100.0 (Lead time factor) | 100.0 |
Top of red Top of red = Red = 150.0 | 150.0 |
Top of yellow Top of yellow = 150.0 + 200.0 = 350.0 | 350.0 |
Top of green Top of green = 350.0 + 100.0 = 450.0 | 450.0 |
Average on-hand target Average on-hand = 150.0 + 100.0 ÷ 2 = 200.0 | 200.0 |
The link includes these inputs. Like any web address, it is seen by the site host when opened.
Do I need to order?
Optional. Net flow position = On hand + On order − Qualified demand.
Due today plus any spikes
How it works
ADU and decoupled lead time
Average daily usage (ADU) is how many units you use or sell per day. Decoupled lead time (DLT) is the longest lead time from this item back to the nearest stocked point upstream. Together, ADU × DLT is the demand you expect over one replenishment lead time.
Yellow zone
Yellow = ADU × DLT. It covers average demand during the lead time — the core of the buffer.
Red zone (safety)
Red base = ADU × DLT × lead time factor. Red safety = Red base × variability factor. Red = Red base + Red safety. Longer lead times get a smaller factor because the yellow zone is already large; more variable items get a bigger safety cushion.
Green zone (order size)
Green is the largest of the minimum order quantity, ADU × DLT × lead time factor, and ADU × order cycle. It sets how much you order at a time and how often: you can't order less than the MOQ, an order cycle of N days sizes green to roughly N days of average demand, so on average orders come about that often (actual timing varies with demand), and the lead-time-factor amount keeps orders from becoming too frequent.
Tops and targets
Top of red = Red; top of yellow = Red + Yellow; top of green = Red + Yellow + Green. Average on-hand target = Red + Green ÷ 2. When net flow position drops to top of yellow or below, order up to top of green.
Default factors
The 70/50/30% lead time and 25/50/80% variability factors are common DDMRP-style starting points, not rules. Tune them with experience for your items.
Worked example (the defaults)
ADU 10, DLT 20 days, Medium lead time (50%), Medium variability (50%), MOQ 0, order cycle 7 days.
- Yellow = 10 × 20 = 200.0
- Red base = 10 × 20 × 0.5 = 100.0
- Red safety = 100 × 0.5 = 50.0
- Red = 100 + 50 = 150.0
- Green = max(0, 100, 70) = 100.0
- Top of red = 150.0
- Top of yellow = 150 + 200 = 350.0
- Top of green = 350 + 100 = 450.0
- Average on-hand = 150 + 100 ÷ 2 = 200.0
FAQ
What is ADU?
Average daily usage: the average number of units consumed or sold per day. If you know monthly usage, divide by 30.44 days per month.
What is decoupled lead time?
The longest cumulative lead time between this item and the nearest upstream stock point (or the supplier), in days. It is usually shorter than the full end-to-end lead time because upstream buffers absorb part of it.
How do I choose lead time and variability factors?
Common starting points are 70% / 50% / 30% for short, medium and long lead times, and 25% / 50% / 80% for low, medium and high variability. Start there, watch how often items fall into red or sit above green, and tune with experience.
What is net flow position?
On hand plus on order (open supply) minus qualified demand (demand due today plus any spikes). When it is at or below top of yellow, you order up to top of green.
Is my data uploaded?
No. Calculations and CSV parsing run in your browser, and the numbers and files you enter are never sent to a server, unless you choose to share a link, which carries the single-item inputs in its address. The page has no ads, sign-up or third-party trackers; the site host keeps standard anonymous visit counts.
Is this official DDMRP software?
No. It is an independent calculator based on the publicly described method, not affiliated with or endorsed by the Demand Driven Institute.
Related tools
Want the full picture for all your SKUs?
A fixed-price inventory health and safety-stock checkup: send one export and get a workbook with ABC/XYZ classes, excess and no-movement inventory, safety stock and reorder points, and buffer screening. The analysis is AI-assisted and reviewed and signed off by a CPIM- and DDMRP-certified planner. Ordered and paid through Upwork.
See the checkup on Upwork (from $175)